Welding method for improving fatigue performance of rectangular non-bearing accessory structure

Abstract

According to the welding method for improving the fatigue performance of the rectangular non-bearing accessory structure, firstly, control optimization on macroscopic morphology and control optimization on microstructure uniformity are established; fatigue characteristics of a welding structure of a rectangular non-bearing accessory are converted into a fatigue strength mechanism represented by local microcell cyclic plastic strain accumulated damage controlled by base metal yield strength, and then the base metal is set to be high-strength steel, so that the fatigue performance of the welding structure is improved. According to the welding method for improving the fatigue performance of the rectangular non-bearing accessory structure, the fatigue performance of the welding structure can be converted into a fatigue strength mechanism which is controlled by the yield strength of base metal and is represented by cyclic plastic strain accumulation damage of a local microcell, and the usual concept of the existing industry is broken through.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure. Background Art

[0002] For a structurally intact rolled or heat-treated material, there is a significant positive correlation between its fatigue performance under dynamic loading conditions and the yield strength of the material, and its fatigue failure mechanism is the cumulative damage behavior of local microzone cyclic plastic strain controlled by the yield strength of the base material. However, for welded joints or structures, due to the influence of three key factors: stress concentration at the weld toe caused by the weld geometry, initial fatigue crack sources formed by geometric discontinuities or welding defects in the weld toe and weld, and the superposition of welding residual tensile stress and external load, the fatigue performance will be significantly reduced compared to the base metal material, and the reduction amplitude is related to the influence degree of the above three key factors. In view of this, in the early fatigue design standards for dynamic load structural components, the fatigue S-N curves of welded joints were classified based on a large amount of experimental data accumulation. The fatigue strength level of welded joints or structures of steel materials is not related to the yield strength level of the material, but only related to joint form design, joint detail characteristics, welding quality grade, and post-weld treatment status, etc. For example: in the mainstream EN 1993 standard, IIW-2259-15 standard, DNV-RP-C203 and other standards, a set of S-N curves that can be used for fatigue design are given according to different design forms and quality grades of steel materials, and the stress range values corresponding to the number of cycles of 2*10 6 are extracted from each S-N curve and defined as fatigue strength characteristic values, which are used as the basis for the fatigue design of dynamic load structural components. For example: in the EN 1993 standard, for a double-sided welded full-penetration retained weld joint, the S-N curve corresponds to DC90, and the fatigue strength characteristic value is 90 MPa. Other standards have almost the same definition.

[0003] The invention application with the application number: CN2006100155949 discloses a "spray fusing method for improving the fatigue performance of a welded structure", which uses a spray welding or laser spray fusing method to coat a spraying material on the weld toe part of the welded structure to form a smooth-transition metal coating layer with a coating thickness between 1 mm and 6 mm at the weld toe part, the coating thickness at the weld toe part is thicker than that in the nearby area, and the spraying material is in a molten state.

[0004] The invention application with the application number of: CN 201780008527.0 discloses "a method for improving the fatigue strength of a lap welded joint, a method for manufacturing a lap welded joint, and a lap welded joint". The fatigue strength of the lap welded joint is improved by the following method. In this lap welded joint, the overlapping part of the first steel material overlaps with the overlapping part of the second steel material, and the edge part of the first steel material is welded to the surface of the second steel material by a welded part extending along the edge part. First, with the direction perpendicular to the extension direction of the welded part and parallel to the surface of the second steel material as the reference direction, the movement of the lap welded joint in the reference direction is restricted, and the movement of the first steel material and the second steel material in the plate thickness direction is restricted. In this state, a part of the second steel material is heated to form a molten part in a part of the second steel material. Summary of the Invention

[0005] The purpose of this technical solution is to break the above conventional understanding and establish a welding structure with a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base material.

[0006] To achieve the above technical objectives, the present invention provides a welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure. The technical solution is as follows:

[0007] A welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure,

[0008] The welding method first establishes the control optimization of the macroscopic morphology and the control optimization of the uniformity of the microscopic organizational structure, converts the fatigue characteristics of the welding structure of the rectangular non-load-bearing accessory into a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base material, and then sets the base material as high-strength steel to improve the fatigue performance of the welding structure;

[0009] The establishment of the control optimization of the macroscopic morphology and the control optimization of the uniformity of the microscopic organizational structure are achieved by first controlling the formation of a uniformly spread fillet weld, and then establishing the control optimization for the following four factors,

[0010] The first factor: the transverse fillet weld of the accessory;

[0011] The second factor: the width uniformity of the transverse fillet weld on the base material bottom plate side;

[0012] The third factor: the transition angle of the weld toe of the transverse fillet weld on the base material bottom plate side;

[0013] The fourth factor: the penetration depth of the transverse fillet weld on the base material bottom plate side.

[0014] Furthermore,

[0015] The so-called "control to form a uniformly spread fillet weld" specifically means: aiming at uniformly spreading the weld, smooth transition of the interface, and continuous transition of the corner, establishing a weaving welding process, and differentially controlling the residence time on the base metal bottom plate side and the residence time on the accessory side during the weaving process according to the influence of the molten pool gravity.

[0016] Furthermore,

[0017] Welding is carried out by controlling the starting arc and ending arc positions within the area of the longitudinal fillet weld of the accessory to avoid the main influence area for transferring loads.

[0018] Furthermore,

[0019] The residence time on the accessory side is controlled within 0.4 - 1.0 s;

[0020] The residence time on the base metal bottom plate side is controlled within 0.2 - 0.5 s.

[0021] Furthermore,

[0022] The optimization of the fillet weld of the accessory is established by establishing the control of the average width of the weld bead on the base metal bottom plate side, establishing the control of the average width of the weld bead on the accessory side, and establishing the control of the bulge height of the transverse fillet weld of the accessory;

[0023] The specific control steps are as follows:

[0024] Firstly, establish a constraint on the average value of the weld bead values on the base metal bottom plate side at at least five equally spaced positions in the width direction,

[0025] Then, establish a constraint on the ratio of the average value of the weld bead values on the base metal bottom plate side at at least five equally spaced positions in the width direction to the average value of the weld bead values on the accessory side at at least five positions in the width direction,

[0026] Finally, establish a constraint on the bulge height of the transverse fillet weld of the accessory.

[0027] Furthermore,

[0028] The establishment of the constraint on the average value of the weld bead values on the base metal bottom plate side at at least five equally spaced positions in the width direction specifically means:

[0029] Control the average value of the weld bead values on the base metal bottom plate side at at least five equally spaced positions in the width direction to be less than 20 mm;

[0030] Accordingly, the establishment of the constraint on the ratio of the average value of the weld bead values on the base metal bottom plate side at at least five equally spaced positions in the width direction to the average value of the weld bead values on the accessory side at at least five equally spaced positions in the width direction specifically means: control the ratio within the range of 1.5 - 2.7;

[0031] Accordingly, the constraint on the convex height of the transverse fillet weld of the accessory is specifically as follows: the convex height is controlled within the range less than 0.25 times the average value of the side fillet weld values of the accessory at at least five equally spaced positions in the width direction.

[0032] Furthermore,

[0033] The control optimization of the width uniformity of the transverse fillet weld on the base metal bottom plate side is specifically as follows:

[0034]

[0035] In the above formula,

[0036] l pi : the equally spaced width values of the transverse fillet weld on the base metal bottom plate side in the width direction, unit: mm; i≥5;

[0037] The average value of i width values, unit: mm.

[0038] Furthermore,

[0039] The control optimization of the weld toe transition angle of the transverse fillet weld on the base metal bottom plate side is specifically to control the weld toe transition angle of the transverse fillet weld on the base metal bottom plate side to be greater than 145°.

[0040] Furthermore,

[0041] The control optimization of the penetration depth of the transverse fillet weld on the base metal bottom plate side is specifically as follows:

[0042] The penetration depth dimension is controlled within the closed interval range of [1.5, 4.5] mm;

[0043] Meanwhile, it satisfies that the penetration depth is greater than

[0044] Furthermore,

[0045] Long arc welding is adopted for welding,

[0046] The wire diameter is controlled to be 1.2 mm,

[0047] The wire extension length is controlled within the range of 18 - 27 mm,

[0048] The welding current is controlled within the range of 150 - 200 A,

[0049] The welding voltage is controlled within the range of 20 - 28 V,

[0050] The welding speed is controlled within the range of 180 - 300 mm / min.

[0051] Furthermore,

[0052] By arranging a circulating water cooling device on the back of the base metal bottom plate, a contact conduction heat exchange with the circulating water temperature less than 45°C during the welding process is provided, and accordingly, a control of the angular deformation of the welded structure less than 5° is established.

[0053] A welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure according to the present invention can convert the fatigue performance of the welded structure into a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base metal, breaking through the conventional concepts of the existing industry. Through the design of the accessory welded structure parameters and the optimization of the welding process specifications, the fatigue performance of the accessory welded structure is ensured, thereby breaking through the limitations of the existing standards for the design of dynamic load structural members, providing an important basis for the lightweight weight reduction of high-strength steel in the design and manufacture of dynamic load structural members, boosting the reduction of the overall manufacturing cost of structural members in the industry, leading to the improvement of the industry manufacturing level and the overall technological progress. Based on the current mainstream welding process method for dynamic load structural members, it will not increase the on-site manufacturing cost and implementation difficulty additionally, is convenient to operate, has a high reproducibility, and is suitable for wide promotion in related industrial fields. It provides technical support for the application and promotion of high-strength steel in multiple industrial fields involving dynamic load service. Replacing ordinary carbon steel with high-strength steel, in the long run, both the manufacturing process and the service process have the effects of green and low carbon, and it will make a lasting contribution to the industrial field to achieve energy conservation and carbon reduction, reflecting important economic value and social value. Brief Description of the Drawings

[0054] Figure 1 is the front view of the welded structure of the present invention;

[0055] Figure 2 is Figure 1 the top view of

[0056] Figure 3 is the design schematic diagram of the leg size of the transverse fillet weld of the accessory for forward transfer of load in the present invention;

[0057] Figure 4 is the design schematic diagram of the penetration depth of the transverse fillet weld on the side of the base metal bottom plate in the present invention;

[0058] Figure 5 is the structure and size schematic diagram of the fatigue evaluation specimen of the rectangular accessory welded structure on the thick bottom plate of Q5000MD high-strength steel in the embodiment of the present invention;

[0059] Figure 6 is Figure 5 the top view of

[0060] In the figure,

[0061] 1 - Base metal bottom plate;

[0062] 2 - Rectangular accessory;

[0063] 3 - Transverse fillet weld of accessory for forward - transferred load;

[0064] 4 - Longitudinal fillet weld of accessory. Specific implementation manner

[0065] Next, according to the accompanying drawings of the specification and the specific implementation manner, a welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure of the present invention will be further specifically described.

[0066] To fully understand this technical solution, the following will specifically introduce this technical solution in two parts. The first part refers to the overview of this technical solution, and the second part refers to the specific process and principle based on the overview.

[0067] Technical overview:

[0068] The R & D team of the applicant found through research that: under certain conditions, when establishing control and optimization of the welding stress concentration effect, establishing control and optimization of the initial fatigue crack source, and establishing control and optimization of the welding residual tensile stress, a comprehensive control and optimization effect can be found, enabling the fatigue performance of the welded structure to be transformed into a fatigue strength mechanism characterized by local micro - area cyclic plastic strain cumulative damage controlled by the yield strength of the base material. Then, based on the positive correlation between the fatigue strength and static load strength of the metal, the material to be welded is set as high - strength steel, thereby improving the fatigue performance of the welded structure. In specific practice, only by controlling the process and setting the working conditions in advance to make the duration of the residual stress relaxation effect generated by the superposition of the welding residual tensile stress and the external load meet the set requirements, can the fatigue performance of the welded structure be improved through the welding of this technical solution. The so - called making the duration of the residual stress relaxation effect generated by the superposition of the welding residual tensile stress and the external load meet the set requirements specifically means controlling that no fatigue failure occurs during 1000 - 5000 cycles of the formation of early fatigue cracks.

[0069] A welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure of this technical solution first establishes control and optimization of the macroscopic morphology and control and optimization of the uniformity of the microscopic organizational structure (the main purpose is to reduce stress concentration during load transfer and reduce the initial fatigue crack source), transforms the fatigue characteristics of the welded structure of the rectangular non - load - bearing accessory into a fatigue strength mechanism characterized by local micro - area cyclic plastic strain cumulative damage controlled by the yield strength of the base material, and then sets the base material to be welded as high - strength steel to improve the fatigue performance of the welded structure;

[0070] The establishment of control and optimization of the macroscopic morphology and control and optimization of the uniformity of the microscopic organizational structure are achieved by first controlling the formation of a uniformly spread fillet weld and then establishing control and optimization for the following four factors

[0071] The first factor: transverse fillet weld of the accessory

[0072] The second factor: uniformity of the width of the transverse fillet weld on the base metal bottom plate side

[0073] The third factor: transition angle of the weld toe of the transverse fillet weld on the base metal bottom plate side

[0074] The fourth factor: penetration depth of the transverse fillet weld on the base metal bottom plate side

[0075] Among them, the control and optimization of the first factor are achieved by establishing the optimization of three parameters: the average fillet width of the base metal bottom plate side, the average fillet width of the accessory, and the protrusion height of the transverse fillet weld of the accessory. See the specific process part below for details. Correspondingly, for the optimization of the second factor, the third factor, and the fourth factor, see the specific process part below for details.

[0076] Specific process and principle:

[0077] This technical solution is oriented to the design and manufacturing field of large structural components serving in dynamic load scenarios. For the non-load-bearing accessory structure welded to the base metal of the structural component, which is used for pipeline or cable layout fixation, operation monitoring and maintenance, decoration, etc., based on the basic principle that the control of the accessory welding structure detail characteristic parameters can appropriately improve its fatigue performance, with the transverse fillet weld of the accessory with a positive load transfer function as the main optimization object, through the design of the fillet size of the transverse fillet weld of the accessory, the design of the fillet width uniformity and the weld toe transition angle of the transverse fillet weld on the base metal bottom plate side, the design of the penetration depth of the transverse fillet weld on the base metal bottom plate side, the optimization of the welding process specifications, etc., a non-load-bearing accessory welding structure with high fatigue performance is obtained, so as to ensure the overall fatigue service safety of the large steel structure and prevent the accessory welding structure from becoming a weak link in the overall structure fatigue service. Specifically as follows:

[0078] Step 1: Design of the fillet size of the transverse fillet weld of the accessory

[0079] Figure 1 、 2 The figure shows a schematic diagram of a typical rectangular accessory welding structure on the large steel structure mother plate. In the figure, 1 is the base metal bottom plate; 2 is the rectangular accessory; 3 is the transverse fillet weld of the accessory for positive load transfer; 4 is the longitudinal fillet weld of the accessory.

[0080] During the overall fatigue service of large steel structures, the fillet welds of accessories do not need to bear positive loads. However, the transverse fillet weld 3 of the accessories has the function of positively transmitting external loads. In the direction of load transmission, the existence of the transverse fillet weld 3 causes significant stress concentration, thereby reducing the fatigue load-bearing capacity of the overall structure. However, the longitudinal fillet weld 4 of the accessories is located laterally. Compared with the transverse fillet weld 3, the stress concentration effect in the direction of load transmission can be ignored. Therefore, the design of the transverse fillet weld 3 of the accessories with the function of positively transmitting loads is very important for the fatigue service characteristics of the overall structure. Figure 3 The figure shows a schematic diagram of the fillet size design of the transverse fillet weld 3 of the accessory for positive load transmission, which mainly includes three design parameters: the average width of the fillet weld on the base metal bottom plate side The average width of the fillet weld on the accessory side The raised height h of the transverse fillet weld. Here, is the arithmetic mean of the measured values of the equally spaced fillet weld widths in the width direction of the transverse fillet weld on the base metal bottom plate side, is the arithmetic mean of the measured values of the equally spaced fillet weld widths in the width direction of the transverse fillet weld on the accessory side. The measured values of the equally spaced fillet weld widths are not less than 5; the width direction here refers to the width direction of the fillet weld, that is, the width direction on the side where the fillet weld positively transmits loads. In order to control the stress concentration degree of the transverse fillet weld of the accessory during the load transmission process and ensure the fatigue performance during service, the fillet size and the raised height of the fillet weld are optimized. and Here, by adopting a differential ratio design of the fillet weld widths on the base metal side and the accessory side and restricting the raised height of the fillet weld, the stress concentration degree of the transverse fillet weld of the accessory during the load transmission process can be minimized, and its fatigue performance can be ensured. If is too high, it not only increases the difficulty of welding process implementation, but also promotes early root cracking during fatigue service due to the too small fillet weld width on the accessory side, which is not conducive to improving the fatigue life of the overall structure. If is too low, it increases the stress concentration at the weld toe on the base metal side during the positive load transmission process, reducing the fatigue performance of the overall structure. If h is too large, the sharp transition formed at the weld toe of the fillet weld also increases the stress concentration degree, reducing the fatigue performance of the overall structure.

[0081] Step 2: Design of the uniformity of the fillet weld width and the weld toe transition angle of the transverse fillet weld on the base metal bottom plate side

[0082] According to the stress concentration characteristics during the service of the accessory welding structure, the weld toe of the transverse fillet weld on the base metal bottom plate side in the as-welded state is often the main stress concentration point and fatigue failure occurs first, and the uniformity of the fillet weld width of the transverse fillet weld has an important influence on the formation of early fatigue cracks. In view of this, the following restrictions are imposed on the uniformity of the fillet weld width of the transverse fillet weld on the base metal bottom plate side:

[0083] Here, l pi is the equally-spaced measurement value of the transverse fillet weld on the base plate side of the base material in the width direction, i≥5, is the arithmetic mean of the equally-spaced measurement values of the transverse fillet weld on the base plate side of the base material in the width direction.

[0084] The weld toe transition angle θ of the transverse fillet weld on the base plate side of the base material directly reflects the spreading uniformity of the fillet weld and has an important influence on the stress concentration degree during the forward transmission of the load. As Figure 3 shown. The following optimization design is carried out for the weld toe transition angle θ of the transverse fillet weld on the base plate side of the base material: θ>145°.

[0085] Since the stress concentration effect of the longitudinal fillet weld of the accessory during the load transmission process is small, no special restrictions are imposed on the detailed characteristics of the longitudinal fillet weld.

[0086] Step 3. Design of the penetration depth of the transverse fillet weld on the base plate side of the base material

[0087] The penetration depth d of the transverse fillet weld of the accessory on the base plate side of the base material can not only change the local tissue characteristics and residual stress field of the base material, but also has a certain influence on the spreading characteristics of the surface weld. As Figure 4 shown. The optimization design of the penetration depth size is as follows: 1.5mm≤d≤4.5mm, and if the penetration depth d is too small, the bonding degree between the accessory and the base plate is weak, and the risk of lack of fusion increases due to local fluctuations in the width direction of the fillet weld, thus becoming an early crack source during the fatigue service process of the overall structure, which is not conducive to ensuring the overall fatigue performance. If the penetration depth d is too large, it will not only increase the range of non-equilibrium tissue and performance areas in the joint area of the base material and the welding residual stress, increasing the risk of fatigue failure, but also the excessive penetration depth will increase the sharpness of the weld toe transition of the surface weld, thus increasing the stress concentration during the forward transmission of the load, which is also not conducive to ensuring the fatigue performance. Since the penetration depth of the longitudinal fillet weld of the accessory has no direct influence on the structure fatigue, no special restrictions are imposed on it.

[0088] Step 4. Optimization of the welding process specifications of the accessory structure

[0089] Considering the operating habits and implementation convenience in the field of large steel structure parts manufacturing, the semi-automatic welding with a flux-cored wire for gas shielded arc welding is used to complete the welding of the circumferential closed fillet weld of the rectangular accessory welding structure. In view of the importance of the transverse fillet weld of the accessory for forward transmission of the load in ensuring the fatigue performance of the overall structure, the following principles are followed for the welding of the fillet weld of the accessory structure:

[0090] (1) Avoid starting and stopping the arc at the transverse fillet weld for load transmission, and the starting and stopping positions should be located at the longitudinal fillet weld of the accessory;

[0091] (2) By means of appropriate welding torch oscillation and edge dwell control, ensure that the circumferential fillet welds of the accessory, especially the transverse fillet welds that transfer loads in the forward direction, are evenly spread and smoothly transitioned on the thick-walled base metal floor plate, avoiding the formation of undercut and sharp transition weld beads. At the same time, ensure that the weld beads at the four corners are evenly and continuously transitioned;

[0092] (3) Install a circulating water cooling device on the back of the base metal floor plate to ensure that the circulating water temperature is less than 45°C. Through forced cooling during the welding process of the accessory structure, reduce the influence of welding heat on the deformation of the overall structure, and control the angular deformation ɑ of the overall structure to be less than 5°.

[0093] Use the commonly used AWS A5.29 E71T1 gas shielded flux-cored wire in the industrial field, with a diameter of 1.2 mm, and apply the following optimized welding process parameters:

[0094] The welding current I = 150 - 200 A, the welding voltage U = 20 - 28 V, the welding speed v = 180 - 300 mm / min, and the welding shielding gas uses an argon-rich mixed gas of 80% Ar + 20% CO 2 ₂. The gas flow rate f = 15 - 25 L / min. According to the actual molten pool flow characteristics and weld bead formation characteristics, combined with the design principles of the characteristic parameters of the transverse fillet welds of the accessory that transfer loads in the forward direction, adopt a differential rapid oscillation method of the welding torch on both sides during the welding process to avoid excessive protrusion at the center of the weld bead and reduce the overall height of the fillet weld. The swing dwell time on the side of the base metal floor plate with the action of forward load transfer is 0.2 - 0.5 s, and the swing dwell time on the accessory side is 0.4 - 1.0 s, so as to ensure the even spread of the transverse fillet welds of the accessory on the side of the base metal floor plate; the different settings of the dwell time here are considered based on the influence of the molten pool gravity, and the internal mechanism of the influence of the molten pool gravity is as follows: during the welding process near the horizontal welding position, the molten pool tends to flow downward due to the action of gravity, so the dwell time is increased at the upper edge, and the arc force is used to hold the molten pool, thereby appropriately increasing the amount of cladding metal at this position and appropriately offsetting the amount of cladding metal flowing downward under the action of gravity; while at the lower edge, due to the action of gravity, there is already an accumulation of the amount of cladding metal. If the edge dwell time is too long, the increased amount of cladding metal will be too much, resulting in too high a weld bead height and protrusion at this position, exacerbating the sharp transition and stress concentration at the adjacent weld toe position between the lower part of the fillet weld and the high-strength steel base metal, which is not conducive to the fatigue performance of the welded structure of this accessory.. In order to reduce the penetration depth of the fillet weld and improve its even spreading ability, use long-arc welding, and control the wire extension length within 18 - 27 mm.

[0095] Example

[0096] The welding method for improving the fatigue performance of the rectangular non - load - bearing accessory structure of the present invention was implemented to verify the feasibility of the technical solution. A Q500MD high - strength steel base plate with a wall thickness of 20 mm was used as the base material. According to the specific steps described in the present invention, the fillet size design of the transverse fillet weld of the accessory, the uniformity of the fillet width and the design of the weld toe transition angle of the transverse fillet weld on the side of the base plate of the base material, the penetration depth design of the transverse fillet weld on the side of the base plate of the base material, and the optimization of the welding process specifications were completed in sequence, and a welded structure of the accessory with good welding quality was obtained. For this welded structure of the accessory, a pull - pull dynamic load fatigue performance verification test was carried out under the conditions of stress ratio R = 0.5 and fatigue stress range Δσ = 80 MPa. The test stop condition was that the test frequency decreased significantly due to the generation of fatigue cracks in the specimen or the number of cycles reached 1*10 7 times. Through the comparison of the test results under this fatigue test condition with the current mainstream standard design values, the optimization effect of the method described in the present invention on the fatigue performance of the welded structure of the accessory was comprehensively evaluated.

[0097] Figure 5 、 6 Figure 8 shows an example of the type and size of the fatigue evaluation specimen of the welded structure of the rectangular accessory located on the Q500MD high - strength steel base plate. The Q500MD thick - wall base plate was machined to ensure that the roughness Ra of the two cross - sections parallel to the loading direction was ≤3.2. The rectangular accessory was also machined to ensure the flatness of the contact surface between the bottom of the accessory and the thick - wall base plate of the base material, and the fitting gap was less than 1 mm. To ensure the welding quality of the circumferential fillet weld of the accessory in the subsequent process, the relevant areas including the thick - wall base plate and the accessory were polished and cleaned before welding to remove rust, oil and other pollutants that may cause a reduction in weld quality. The area to be welded showed obvious metallic luster.

[0098] In this embodiment, considering the operating habits and implementation convenience in the field of large - scale steel structure manufacturing, the circumferential closed fillet weld of the welded structure of the rectangular accessory was welded by a semi - automatic flux - cored wire gas - shielded arc welding. In view of the importance of the transverse fillet weld of the accessory that transmits the load in the positive direction to ensuring the fatigue performance of the overall structure, the following principles were followed for the fillet weld welding of the accessory structure:

[0099] (1) Avoid starting and stopping arcs at the transverse fillet weld that transmits the load. The starting and stopping arc positions should be located at the longitudinal fillet weld of the accessory;

[0100] (2) Through appropriate welding torch oscillation and edge stay control, ensure that the circumferential fillet weld of the accessory, especially the transverse fillet weld that transmits the load in the positive direction, spreads evenly and transitions smoothly on the thick - wall base plate of the base material, avoiding the formation of undercut and sharp transition weld beads. At the same time, ensure that the weld beads at the four corners are evenly and continuously transitioned;

[0101] (3) A circulating water cooling device is arranged on the back of the base metal bottom plate to ensure that the circulating water temperature is less than 45 °C. During the welding process of the accessory structure, forced cooling is carried out to reduce the influence of welding heat on the deformation of the overall structure, and the angular deformation ɑ of the overall structure is controlled to be less than 5 °.

[0102] The commonly used AWS A5.29 E71T1 gas shielded flux cored wire in the industrial field is adopted, with a diameter of 1.2 mm. The optimized welding process parameters are as follows:

[0103] The welding current I = 160 - 180 A, the welding voltage U = 23 - 26 V, the welding speed v = 190 - 220 mm / min. The welding shielding gas is an argon-rich mixed gas of 80% Ar + 20% CO 2 and the gas flow rate f = 18 - 20 L / min. In order to obtain an accessory fillet weld with smooth transition and uniform spreading at the weld toe edge, according to the actual molten pool flow characteristics and weld formation characteristics, combined with the design principle of the characteristic parameters of the accessory transverse fillet weld for forward transfer of load, a rapid swing method of the welding torch with differences on both sides is adopted during the welding process, avoiding excessive protrusion at the weld center and reducing the overall height of the fillet weld. The swing residence time on the base metal bottom plate side with the function of forward transfer of load is 0.2 - 0.4 s, and the swing residence time on the accessory side is 0.6 - 0.9 s, ensuring uniform spreading of the accessory transverse fillet weld on the base metal bottom plate side. In order to reduce the penetration depth of the fillet weld and improve its uniform spreading ability, long arc welding is adopted, and the wire extension length is controlled at 20 - 24 mm. By arranging a circulating water cooling device on the back of the base metal bottom plate, it is ensured that the angular deformation ɑ of the accessory welding structure fatigue verification specimen after welding is less than 5 °. Table 1 shows the characteristic parameters of the accessory transverse fillet weld for forward transfer of load obtained in the embodiment. Table 2 shows the conditional fatigue life of the three groups of accessory welding structures when the stress ratio R = 0.5 obtained in the embodiment. It can be seen that under the condition of the design stress range Δσ = 80 MPa commonly used in the current mainstream standard, the number of cycles obtained in the test of the accessory welding structure in the embodiment is much higher than the corresponding number of cycles in the design standard. Through the implementation of the welding method for the non-load-bearing accessory structure described in the present invention and comparing and contrasting its fatigue performance data under specific conditions with the design values of the current mainstream standard, it is confirmed that the welding method for the non-load-bearing accessory structure described in the present invention has the characteristic of high fatigue performance.

[0104] Table 1 Characteristic parameters of the accessory transverse fillet weld for forward transfer of load

[0105]

[0106] Table 2 Conditional fatigue life of the three groups of accessory welding structures

[0107]

[0108] Note: The corresponding number of cycles for the design standard is the number of cycles corresponding to the fatigue stress range Δσ = 80 MPa on the typical rectangular attachment fatigue S-N curve specified in EN 1993 standard. This stress range value is also commonly used in the fatigue design of structural members.

Claims

1. A welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure, characterized in that: The welding method first establishes the control optimization of the macroscopic morphology and the control optimization of the uniformity of the microscopic organizational structure, converts the fatigue characteristics of the welded structure of the rectangular non - load - bearing accessory into a fatigue strength mechanism characterized by the cumulative damage of local micro - area cyclic plastic strain controlled by the yield strength of the base metal, and then sets the base metal as high - strength steel to improve the fatigue performance of the welded structure; The establishment of the control optimization of the macroscopic morphology and the control optimization of the uniformity of the microscopic organizational structure are achieved by first controlling the formation of a uniformly spreading fillet weld and then establishing the control optimization for the following four factors, The first factor: the transverse fillet weld of the accessory; The second factor: the width uniformity of the transverse fillet weld on the base metal bottom plate side; The third factor: the weld toe transition angle of the transverse fillet weld on the base metal bottom plate side; The fourth factor: the penetration depth of the transverse fillet weld on the base metal bottom plate side.

2. The welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure according to claim 1, characterized in that: The "control of forming a uniformly spreading fillet weld" is specifically: for the purpose of uniform weld spreading, smooth interface transition and continuous transition at the corner, a weaving welding process is established, and the residence time on the base metal bottom plate side and the residence time on the accessory side during the weaving process are differentially controlled according to the influence of the molten pool gravity.

3. The welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure according to claim 2, characterized in that: During welding, the starting and ending arc positions are controlled in the area of the longitudinal fillet weld of the accessory to avoid the main influence area of the transmitted load.

4. The welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure according to claim 2, characterized in that: The residence time on the accessory side is controlled within 0.4 - 1.0 s; The residence time on the base metal bottom plate side is controlled within 0.2 - 0.5 s.

5. The welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure according to claim 1, characterized in that: The establishment of the optimization of the accessory fillet weld is achieved by establishing the control of the average width of the weld bead on the base metal bottom plate side, establishing the control of the average width of the weld bead on the accessory side, and establishing the control of the protrusion height of the transverse fillet weld of the accessory; The specific control steps are as follows: First, a constraint is established for the average value of the weld bead values on the base metal bottom plate side at at least five equally - spaced positions in the width direction, Then, a constraint is established for the ratio of the average value of the weld bead values on the base metal bottom plate side at at least five equally - spaced positions in the width direction to the average value of the weld bead values on the accessory side at at least five positions in the width direction, Finally, a constraint is established for the protrusion height of the transverse fillet weld of the accessory.

6. The welding method for improving the fatigue performance of a rectangular non - load - bearing accessory structure according to claim 5, characterized in that: The establishment of the constraint for the average value of the weld bead values on the base metal bottom plate side at at least five equally - spaced positions in the width direction is specifically: Controlling the average value of the weld bead values on the base metal bottom plate side at at least five equally - spaced positions in the width direction to be less than 20 mm; Accordingly, a constraint is established on the ratio of the average value of the side fillet weld angles of the base material bottom plate at at least five equally spaced positions in the width direction to the average value of the side fillet weld angles of the accessory at at least five equally spaced positions in the width direction, specifically: controlling the ratio within the range of 1.5 to 2.7; Accordingly, a constraint is established on the convex height of the transverse fillet weld of the accessory, specifically: controlling the convex height within the range less than 0.25 times the average value of the side fillet weld angles of the accessory at at least five equally spaced positions in the width direction.

7. A welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure according to claim 1, characterized in that: The establishment of control optimization for the width uniformity of the transverse fillet weld on the side of the base material bottom plate is specifically: In the above formula, l pi : The width value at equal intervals in the width direction of the transverse fillet weld on the base metal bottom plate side, unit: mm; i ≥ 5; The average value of the width of i, unit: mm.

8. A welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure according to claim 1, characterized in that: The establishment of control optimization for the weld toe transition angle of the transverse fillet weld on the side of the base material bottom plate is specifically to control the weld toe transition angle of the transverse fillet weld on the side of the base material bottom plate to be greater than 145°.

9. A welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure according to claim 7, characterized in that: The establishment of control optimization for the penetration depth of the transverse fillet weld on the side of the base material bottom plate is specifically: Controlling the penetration depth dimension within the closed interval range of [1.5, 4.5] mm; While satisfying that the penetration depth is greater than 10. A welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure according to claim 1, characterized in that: Long arc welding is used for welding, Controlling the wire diameter to be 1.2 mm, Controlling the wire extension length within the range of 18 - 27 mm, Controlling the welding current within the range of 150 - 200 A, Controlling the welding voltage within the range of 20 - 28 V, Controlling the welding speed within the range of 180 - 300 mm / min.

11. A welding method for improving the fatigue performance of a rectangular non-load-bearing accessory structure according to claim 1, characterized in that: By arranging a circulating water cooling device on the back of the base material bottom plate to provide contact conduction heat exchange with the circulating water temperature less than 45°C during the welding process, accordingly, a control of less than 5° for the angular deformation of the welding structure is established.

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